連天可裝 It Can Bottle the Sky
我這葫蘆，連天都裝在裡面哩。」那怪道：「就可以裝天？」行者道：「當真的裝天。」那怪道：「只怕是謊，就裝與我們看看才信；不然，決不信你。」行者道：「天若惱著我，一月之間，常裝他七八遭，不惱著我，就半年也不裝他一次。」我这葫芦，连天都装在里面哩。」那怪道：「就可以装天？」行者道：「当真的装天。」那怪道：「只怕是谎，就装与我们看看才信；不然，决不信你。」行者道：「天若恼着我，一月之间，常装他七八遭，不恼着我，就半年也不装他一次。」
逐句解 Line by line
"This gourd of mine can bottle up the very sky inside it."
連天都裝 (lián tiān dōu zhuāng), "bottles even the sky" -- 連...都 is the ordinary "even X" frame, and the 哩 (li) keeps it offhand. The lie is deliberately too big to check, which is what makes it work.
The imps said: "It can really bottle the sky?"
就可以裝天 (jiù kě yǐ zhuāng tiān), "it can actually bottle the sky?" Disbelief is exactly the reaction Pilgrim ordered, because disbelief asks for proof, and proof is what he means to stage.
Pilgrim said: "Truly it bottles the sky."
當真 (dāng zhēn), "in earnest." Four words, no elaboration, straight face. Over-explaining would sink it.
The imps said: "We fear it's a lie — bottle it for us to see, and then we'll believe you; otherwise we certainly won't."
只怕是謊 (zhǐ pà shì huǎng), "we suspect a lie." 才信 (cái xìn), "only then will we believe." They have now demanded the demonstration, which means the demonstration is their idea.
Pilgrim said: "When Heaven vexes me, I'll bottle it seven or eight times in a month; when it doesn't, I won't bottle it once in half a year."
The masterstroke is the shrug. 惱著我 (nǎo zhe wǒ), "when it annoys me," takes the 著 of an ongoing state; 七八遭 (qī bā zāo), "seven or eight times." Bottling Heaven is presented as a mildly tiresome chore he does when provoked and skips when he is not -- and nothing sells an impossible claim like being bored by it.
Pilgrim raises the stakes to the absurd: not a thousand men but the sky itself. The claim is preposterous, and the imps' natural response -- prove it -- is precisely the move he has been steering them toward. A cruder trickster would have grabbed the treasures and run. Pilgrim maneuvers his victims into demanding the very demonstration that will let him win them in what looks like a fair exchange.
The masterstroke is the offhand elaboration. Seven or eight times a month when Heaven annoys him; not once in half a year when it does not. The false casualness is what sells it, because a man who could not do the thing would never speak of it so lightly. What is on display here is not magic but performance -- the confidence man's instinct for the detail that makes the impossible sound like a chore.